Electrical brush assembly



March 3, 1964 c. E. JACKSON ELECTRICAL BRUSH ASSEMBLY Filed March 6, 1962 INVENTOR 0027/5 f Jhc/rJo/v BY United States Patent 3,123,732 ELE CTRECAL BRUSH ASSEMBLY (Zurtis E. Jackson, Essex Fells, Ni, assignor to The Haven Company, Livingston, Ni, a corporation of Delaware Filed Mar. 6, 1962, Ser. No. 177,777 10 Claims. (*Ci. 310-4247) The present invent-ion relates to electrical brush assemblies and, particularly, to such assemblies adapted in operation to conduct large values of electrical current.

It is an object of the invention to provide a new and improved electrical brush assembly and one which in use provides a protective limit upon longitudinal brush movement due to normal end-surface brush wear and thereby avoids the danger of undesirable scoring of a commutator surface with which the brush assembly is used.

It is a further object of the invention to provide a novel electrical brush assembly having a member operative to limit the ultimate extent of brush wear and to position and guide a helical spring which biases the brush into engagement with an associated commutator surface, such member also being effective visually to indicate the prevailing extent of brush wear during a prolonged period of brush use.

It is an additional object of the invention to provide an electrical brush assembly of the laminar brush type and one adapted in operation to conduct large values of electrical current with relatively low values of electrical losses and relatively uniform current density in each unit of cross-sectional brush area.

Other objects and advantages of the invention will appear as the detailed description thereof proceeds in the light of the drawing forming a part of this application and in which:

FIGS. 1 and 2 illustrate respective top and side-elevational views of an electrical brush assembly embodying the present invention;

FIG. 3 is a cross-sectional view of the brush assembly taken along the plane 33 of FIG. 2; and

FIGS. 4 and 5 are cross-sectional views taken along the respective planes 4-4 of FIG. 1 and 5-5 of FIG. 2 and illustrate certain constructional details of an electrical brush assembly embodying the present invention.

Referring now more particularly to FIGS. 1-3, the electrical brush assembly of the present invention includes a brush holder 1% having a central bore 11 of rectangular cross-section in which three carbon brushes i2, 13 and 14 are positioned and guided for longitudinal movement. Each such brush has an elongated flexible wire conductor 15 mechanically and electrically secured at one end, and in conventional manner, to an end of the associated one of the brushes. The remote end of each such wire lead is mechanically crimped between and soldered to an upturned end portion of a flange 16 provided along the edge of a guide member 17. One end of the brush holder lid is provided with integral hollow opposed bridges 18 and i9, and the guide member 17 and an electrical connector plate 29 are secured by machine screws 21 to the bridges l8 and 19 of the holder as shown. The connector plate 20* has a looped end 22 which is adapted to be crimped over and soldered to a wire conductor of large current capacity and which connects the brush assembly in an electrical circuit.

The holder id conveniently is of cast metal and may be secured to a supporting disc 23 of insulating material by machine screws 24 extending through apertures 25 of the disc and engaging threaded apertures 26 of the holder. The holder has integrally formed cooling fins 27, and is provided with a port 28 which is aligned with an aperture 29 provided in the insulating disc 23 and through which forced cooling air is blown to cool the brush holder 3,123,732 Patented Mar. 3, 1964 during operation. As also shown in FIGS. 1 and 3, the walls of the bore 11 of the holder 10 have longitudinal grooves 30 which reduce the frictional forces exerted under operational conditions by the walls of the bore upon the exterior surfaces of the brushes 12, 13 and 14. The advantage of this will be perceived more clearly in connection with the description hereinafter of the differential spring bias under which the brushes operate.

Certain details of the brush assembly construction are illustrated more clearly by the cross-sectional views of FIGS. 4 and 5. It was previously explained that one end of each of the elongated flexible wire conductors 15 is mechanically and electrically secured to an end of an associated brush. This, as shown in FIGS. 4 and 5, is the end 15a of each conductor 15 which is shown as embedded in conventional manner in the upper end of an individual one of the brushes. The brush assembly includes a plurality of elongated hollow metallic tubes 31 which are positioned upon and enclose a length of an individual one of the conductors 15. The tubes 31 are provided with apertures 32 through which each tube is soldered to its associated conductor 15 at a position on the conductor such that the lower end of the tube as seen in FIGS. 4 and 5 is loosely positioned within a bore 33 formed in the upper end of each brush in concentric relation with the conductor 15. This positional relationship restrains the lower end of the tube 31 against substantial radially inward movement with relation to its associated brush but enables a swivel motion of the tube relative to the brush. The brushes 12, 13 and 14 together have a small amount of free side play in the bore 11 of the brush holder, and this play' and the swivelled joint last mentioned enable each brush to have full-area contact with the surface of a commutator member with which the brush assembly is used.

Each of the tubes 31 slidably extends through an individual aperture 34 provided in the guide member 17, and is maintained in assembled relation with the latter by a G-washer 35 engaging a circumferential groove formed near the end of each tube 31. Helical springs 36 are slidably positioned over the tubes 31, and in the assembled state of the tubes 31 and guide member 17 are compressed between the guide member and an associated one of the brushes 12, 13 or 14. The helical springs as bias the associated brushes 12, 13 or 14 into engagement with the surface of the associated rotatable commutator member which in FIG. 5 is indicated in operative relation to the brush assembly by the broken line 37. The direction of commutator rotation is indicated by the brokeiHl-ine arrow 38, and it will be seen that the median planes of the brushes 12, 13 and 14 form a forwardly slanting angle to corresponding radial planes of the commutator.

The use of the plural laminar brush arrangement just described has the important advantage that at least two of the brushes remain in constant engagement with the commutator surface, indicated by the broken line 37, even though one of the brushes might be temporarily raised above the commutator surface by a small body of foreign material which may have become embedded in the commutator surface. It has been found in practice that the rotational motion of the commutator surface past the brushes, in a direction indicated by the arrow 33 in FIG. 5, tends to pack the brushes against each other in the direction of rotation and to press the surface of the last brush 14 against the wall 11 of the holder 113. To insure free movement of the brushes relative to each other under operating conditions and by reason of small commutator imperfections at last mentioned, wall frictional forces are reduced by the grooves 30 and the brushes are differentially spring biased. Thus the spring 36 associated with the brush l3 exerts a larger bias force 3 than does the spring associated with the brush l2, and the spring as associated with the brush l4 exerts a larger bias force than does the spring associated with the brush 13.

When the brush assembly is operatively positioned with relation to the surface of an associated commutator, it will be evident from FIG. 5 that the brushes 12, i3 and 14 when new are so positioned that they fill the bore 11 of the holder ill. in this brush position, the tubes 31 have a substantial portion of their length projecting through the apertures 34 of the guide member 117 and the C-Washers 35 are displaced a substantial distance from the guide member. The tubes 31 thus provide at any time a visual indication of the prevailing extent of Wear of the brushes. Brush wear may continue until the C- Washers 35 engage the guide member 17, and the brushes must then be replaced. This action of the C-washers 35 in limiting the longitudinal movement of the brushes with end Wear thereof has the important result that the brushes are never permitted, through inattention or neglect, to Wear so far that the embedded ends of the Wire conductors 15 come into engagement with the commutator surface 37 and undesirably score it. In practice,'the tubes 31 are substantially longer than they have been shown for simplicity in FIGS. 4 and 5 so that the brushes 12, 13 and 14 are permitted to wear much more than is indicated in these figures of the drawing. The practical extent of wear, however, should not permit the embedded ends 15a of the conductors 15 to contact the surface 37 of the commutator or should not permit the brushes to wear to a length so short that they are no longer properly guided by the bore ll of the holder 10 and thus tend to become wedged in the bore.

The electrical brush assembly just described is suitable for a wide range of diverse applications, but has particular utility in a synchronous electrical switch of the type disclosed in the copending application of John P. Brady, Ser. No. 177,813, filed March 6, 1962, and that also disclosed in applicants copending application Ser. No. 177,- 898, filed March 6, 1962, and both assigned to the same assignee as the present application.

It will be apparent from the foregoing description of the invention that an electrical brush assembly embodying the invention provides a protective limit upon longitudinal brush movement due to its normal end-surface wear and thus prevents damage by scoring of a commutator surface with which the brush assembly is used. At the same time, the assembly provides a positive and accurate visual indication of the prevailing extent of brush wear during a prolonged period of brush use. The brush assembly of the invention is readily adapted in operation to conduct large values of electrical current with relatively uniform current density in each unit crosssectional brush area.

While a specific form of invention has been described for purposes of illustration, it is contemplated that numerous changes may be made without departing from the spirit of the invention.

What is claimed is:

1. An electrical brush assembly comprising, an electrical brush having an elongated flexible wire conductor mechanically and electrically secured at one end to an end of said brush, a hollow elongated tube enclosing a length of said conductor and secured thereto at a position thereon such that one end of said tube is at least closely adjacent said one end of said brush to restrain said tube against significant radially inward movement with relation to said brush but to enable a swivel motion of said tube relative thereto, a guide member having an aperture through which said tube slidably extends upon assembly of said guide member and tube, means for maintaining said guide member and tube in assembled relation by limiting the withdrawal of said tube from said aperture, and means for biasing said brush away from said guide member.

2. An electrical brush assembly comprising, an electrical brush having an elongated flexible wire conductor mechanically and electrically secured at one end to an end of said brush, a hollow elongated tube enclosing a length of said conductor and secured thereto at a position thereon such that one end of said tube is at least closely adjacent said one end or" said brush to restrain said tube against substantial radially inward movement with relation to said brush but to enable a swivel motion of said tube relative thereto, a guide member having an aperture through which said tube slidably extends upon assembly of said guide member and tube, means for maintaining said guide member and tube in assembled rela tion by limiting the withdrawal of said tube from said aperture, and spring means encircling said tube and compressed between said guide member and brush to bias said brush away from said guide member.

3. An electrical brush assembly comprising: an electrical brush having an elongated flexible wire conductor mechanically and electrically secured at one end to an end of said brush; a hollow elongated tube enclosing a length of said conductor and secured thereto at a position thereon such that one end of said tube is at least closely adjacent said one end of said brush to restrain said tube against substantial radially inward movement with relation to said brush but to enable a swivelmotion of said tube relative thereto; a guide member having an aperture through which said tube slidably extends upon assembly of said guide member and tube; a helical wire spring slidably positioned upon said tube; and means for maintaining said guide member, said tube, and said spring in assembled relation with said spring compressed between said guide member and said brush while permitting a range of longitudinal movement of said tube through said aperture of said guide member.

4. An electrical brush assembly comprising: an electrical brush having an elongated flexible wire conductor mechanically and electrically secured at one end to an end of said brush; a hollow elongated tube enclosing a length of said conductor and secured thereto at a position thereon such that one end of said tube is at least closely adjacent said one end of said brush to restrain said tube against substantial radially inward movement with relation to said brush but to enable a swivel motion of said tube relative thereto; a guide member having an aperture through which said tube slidably extends upon assembly of said guide member and tube; a helical wire spring slidably enclosing a length of said tube; and a collar ecured to the other end of said tube to maintain said guide member, said tube, and said spring in assembled relation with said spring compressed between said guide member and brush.

5. An electrical brush assembly comprising, an electrical brush having an elongated flexible wire conductor mechanically and electrically secured at one end to an end of said brush, said end of said brush having a bore concentric with said conductor, a hollow elongated tube enclosing a length of said conductor and secured thereto at a position thereon such that one end of said tube is loosely positioned by said bore to restrain said tube against substantial radially inward movement with relation to said brush but to enable a swivel motion of said tube relative thereto, a guide member having an aperture through which said tube slidably extends upon assembly of said guide member and tube, means for maintaining said guide member and tube in assembled relation by limiting the withdrawal of said tube from said aperture, and means for biasing said brush away from said guide member.

6. An electrical brush assembly comprising, an electrical brush having an elongated flexible wire conductor mechanically and electrically secured at one end to an end of said brush, said end of said brush having a bore concentric with said conductor, a hollow elongated tube enclosing a length of said conductor and secured thereto at a mills position thereon such that one end of said tube is loosely positioned by said bore to restrain said tube against substantial radially inward movement with relation to said brush but to enable a swivel motion of said tube relative thereto, a guide member having an aperture through which said tube slidably extends upon assembly of said guide member and tube, a stop member affixed to the free end of said tube to maintain said guide member and tube in assembled relation by limiting the withdrawal of said tube from said aperture, means positioned by said tube for biasing said brush away from said guide member, and means for electrically and mechanically securing the free end of said conductor to said guide member.

7. An electrical brush assembly comprising, a brush housing having a brush guide bore, an electrical brush movably positioned within said bore and having an elongated flexible wire conductor mechanically and electrically secured at one end to an end of said brush, a hollow elongated tube enclosing a length of said conductor and secured thereto at a position thereon such that one end of said tube is at least closely adjacent said one end of said brush to restrain said tube against significant radially inward movement with relation to said brush but to enable a swivel motion of said tube relative thereto, a guide member atfixed to said housing and having an aperture through which said tube slidably extends upon longitudinal movement of said brush within said bore, stop means on the other end of said tube for maintaining said guide member and tube in assembled relation by preventing the withdrawal of said tube from said aperture and to provide a protective limit upon the extent of longitudinal brush movement due to its normal end-surface wear, and means for biasing said brush away from said guide membet.

8. An electrical brush assembly comprising, a brush housing having a brush guide bore, an electrical brush movably positioned within said bore and having an elongated flexible wire conductor mechanically and electrically secured at one end to an end of said brush, a hollow elongated tube enclosing a length of said conductor and secured thereto at a position thereon such that one end of said tube is at least closely adjacent said one end of said brush to restrain said tube against significant radially inward movement with relation to said brush but to enable a swivel motion of said tube relative thereto, a guide member aifixed to said housing and having an aperture through which said tube slidably extends upon longitudinal movement of said brush within said bore, a stop member afiixed to the other end of said tube for maintaining said guide member and tube in assembled relation by limiting the withdrawal of said tube from said aperture, and to provide a protective limit upon the extent of longitudinal brush movement due to its normal end-surface wear, and a helical wire spring sidably positioned on said tube and compressed between said guide member and brush to bias said brush away from said guide member.

9. An electrical brush assembly comprising, a brush housing having a brush guide bore of rectangular crosssection, a stack of electrical brushes of rectangular crosssection individually movably positioned within said bore and each having an elongated flexible wire conductor mechanically and electrically secured at one end to an end of an individual one of said brushes, a hollow elongated tube individual to each said conductor and enclosing a length thereof, means for securing each said tube at a position on its individual conductor such that one end of said each tube is at least closely adjacent said one end of the associated one of said brushes to restrain said each tube against significant radially inward movement with relation to said associated brush but to enable a swivel motion of said tube relative thereto, a guide member atfixed to said housing and having apertures through which individual ones of said tubes slidably extend upon longitudinal movement of said brushes within said bore, stop means individual to each said tubes for maintaining said guide member and tubes in assembled relation by limiting the withdrawal of said tubes from said apertures and to provide a protective limit upon the extent of longitudinal movement of each brush due to its normal end-surface wear, and means for individually biasing each said brush away from said guide member.

10. An electrical brush assembly comprising, a brush housing having a brush guide bore of rectangular crosssection, a stack of electrical brushes of rectangular crosssection individually movably positioned within said bore and each having an elongated flexible wire conductor mechanically and electrically secured at one end to an end of an individual one of said brushes, a hollow elongated tube individual to each said conductor and enclosing a length thereof, means for securing each said tube at a position on its individual conductor such that one end of said each tube is at least closely adjacent said one end of the associated one of said brushes to restrain said each tube against significant radially inward movement with relation to said associated brush but to enable a swivel motion of said tube relative thereto, a guide member affixed to said housing and having apertures through which individual ones of said tubes slidably extend upon longitudinal movements of said brushes within said bore, stop means individual to each said tubes for maintaining said guide member and tubes in assembled relation by limiting the withdrawal of said tubes from said apertures and to provide a protective limit upon the extent of longitudinal movement of each brush due to its normal end-surface wear, and a plurality of helical wire springs each slidably positioned on an individual one of said tubes for individually biasing each said brush away from said guide member by a bias force increasing in value from brush to brush in a given direction of stacking thereof.

No references cited. 

1. AN ELECTRICAL BRUSH ASSEMBLY COMPRISING, AN ELECTRICAL BRUSH HAVING AN ELONGATED FLEXIBLE WIRE CONDUCTOR MECHANICALLY AND ELECTRICALLY SECURED AT ONE END TO AN END OF SAID BRUSH, A HOLLOW ELONGATED TUBE ENCLOSING A LENGTH OF SAID CONDUCTOR AND SECURED THERETO AT A POSITION THEREON SUCH THAT ONE END OF SAID TUBE IS AT LEAST CLOSELY ADJACENT SAID ONE END OF SAID BRUSH TO RESTRAIN SAID TUBE AGAINST SIGNIFICANT RADIALLY INWARD MOVEMENT WITH RELATION TO SAID BRUSH BUT TO ENABLE A SWIVEL MOTION OF SAID TUBE RELATIVE THERETO, A GUIDE MEMBER HAVING AN APERTURE THROUGH WHICH SAID TUBE SLIDABLY EXTENDS UPON ASSEMBLY OF SAID GUIDE MEMBER AND TUBE, MEANS FOR MAINTAINING SAID GUIDE MEMBER AND TUBE IN ASSEMBLED RELATION BY LIMITING THE WITHDRAWAL OF SAID TUBE FROM SAID APERTURE, AND MEANS FOR BIASING SAID BRUSH AWAY FROM SAID GUIDE MEMBER. 